使用 Jackson 将对象转换为 JSON 时的无限递归

Question

我有这个 class 用来存储工具的首选项。 class 使用 toString() 将自身转换为 JSON。当我将对象转换为 JSON 时出现无限递归错误，我无法弄清楚原因。我没有任何循环引用，所以这让我有点困惑。任何帮助将不胜感激。

这是我的 class 结构：

public class ToolPrefs
{
   private boolean isFloating;
   private ToolPalettePlacement placement; //this is an enum
   private boolean isSelected;
   private int dockLocation;
   private Point dialogLocation;
   private Dimension dialogSize;

   public ToolPrefs(){}

   public boolean isFloating(){return isFloating; }

   public void setFloating(boolean floating){ isFloating = floating; }

   public ToolPalettePlacement getPlacement(){ return placement; }

   public void setPlacement(ToolPalettePlacement placement){ this.placement = placement;}

   public boolean isSelected(){ return isSelected;}

   public void setSelected(boolean selected){isSelected = selected;}

   public int getDockLocation(){return dockLocation;}

   public void setDockLocation(int dockLocation){this.dockLocation = dockLocation; }

   public Point getDialogLocation(){return dialogLocation;}

   public void setDialogLocation(Point dialogLocation){ this.dialogLocation = dialogLocation;}

   public Dimension getDialogSize(){ return dialogSize; }

   public void setDialogSize(Dimension dialogSize){this.dialogSize = dialogSize;}


   @JsonIgnore @Override
   public String toString()
   {
      String json;
      ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
      try
      {
         json = ow.writeValueAsString(this);
      }
      catch (IOException e)
      {
         e.printStackTrace();
         json = "";
      }
      return json;
   }
}

这是我收到的异常片段：

com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (WhosebugError) (through reference chain: java.awt.Point["location"]->java.awt.Point["location"]->java.awt.Point["location"]->java.awt.Point["location"]...) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:518) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:464) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:504) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:117)

Answer 1

您遇到的问题是由于您的对象嵌入了 Point class。

要解决此问题，您可以指示 Jackson 在第一层深度停止，要实施此解决方案，您可以按照以下步骤操作：

1) 首先，你必须是运行 Jackson 的 2.x 版本，我已经用这个测试了解决方案：

<dependencies>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.8.3</version>
    </dependency>
</dependencies>

2) 当您初始化 ObjectMapper 的新实例时，请执行以下操作：

ObjectWriter ow = new ObjectMapper().configure(DEFAULT_VIEW_INCLUSION, true).writer().withDefaultPrettyPrinter();

3) 在你有 Point 类型的地方，使用注解：

@JsonView(Point.class) Point dialogLocation;

Jackson会停在第一关，结果会是：

{
  "dialogLocation" : {
    "x" : 2.0,
    "y" : 3.0
  }
}

更多文档，你可以看这个：

Limit Jackson output to only one level

Enable default view inclusion on Jackson 2.x ObjectMapper

我已经测试了该解决方案，只要您使用 Jackson 的 2.x 版本，它就可以工作。有了 1.x，我还无法做到运行。

使用 Jackson 将对象转换为 JSON 时的无限递归

Infinite Recursion when convert object to JSON using Jackson

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recursion

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infinite

jackson